The invention relates to electronic circuit assemblies for semiconductor chips. The assembly must provide an electrical connection path for current flow through the chip, and must also provide a thermal path to a heat sink to dissipate heat generated by the chip.
Examples of electronic circuit assemblies are shown in my previous U.S. Pat. Nos. 3,958,075, 4,156,148, 4,196,411, 4,215,235, 4,218,724, 4,250,481, 4,257,091, 4,266,140, 4,394,530, 4,449,165, 4,449,292, 4,488,202, 4,498,120, 4,546,410, 4,546,411, 4,554,613, 4,574,162 and 4,577,387, hereby incorporated by reference.
As shown in FIG. 1, it is known in the prior art to mount a silicon semiconductor chip 2 on a molybdenum material layer 4, such as molymanganese, which in turn is mounted on a copper lead frame 6 which in turn is mounted to an electrically insulating ceramic substrate 8 which in turn is mounted to a heat sink 10. Circuit connections are made to the silicon chip and to the copper lead frame at terminals 12 and 14. The current flow path between terminals 12 and 14 is through silicon chip 2 through molybdenum layer 4 and through copper lead frame 6. The thermal path from silicon chip 2 is through molybdenum layer 4 through copper lead frame 6 through ceramic substrate 8 to heat sink 10. Molybdenum layer 4 has a coefficient of thermal expansion close to that of silicon and hence provides a desirable thermal match therewith which prevents cracking of the chip during operation. A trade-off, however, is that the molybdenum constitutes an additional layer through which heat must travel to ceramic substrate 8, and hence increases thermal resistance.
The present invention provides an improvement over the structure of FIG. 1.